2/4/09

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Concrete is a construction material composed of cement as well as other materials generally a coarse aggregate such as gravel, limestone, or granite, plus a fine aggregate such as sand and water. To improve the strength and life time of concrete, it is made denser and less porous, but this leads to greater tendency to crack. National Institute of Standards and Technology engineers have a different approach. They have identified that infiltrating chloride and sulfate ions from road salt, sea water and soils cause internal structural damage over time that leads to cracks and weakening of concrete. Chlorides have been shown to cause chemical changes in cement, leading to loss of strength as well as attacking the steel reinforcement present in most concrete and similarly sulphates in solution in contact with concrete can cause chemical changes to the cement causing significant microstructural effects leading to the weakening of the cement binder. They have suggested to change the viscosity of the solution in the concrete at the microscale to reduce the speed at which chlorides and sulfates enter the concrete by incorporating nano-sized additive that slows down penetration of chloride and sulfate ions. The engineers suggest that the additives can be blended directly into the concrete with current chemical admixtures, but that even better performance is achieved when the additives are mixed into the concrete which can double the concrete's service life.